The structural, electronic and optical properties of RbSnCl3 are investigated by the first-principles calculations. Two new phases of Cm and Imm2 are predicted and the phonon spectrum are analyzed, which shows that the two phases are all dynamically stable. The band edge positions show that the two phases conform to the criteria of photocatalysts for water splitting, and strains are added to the two phases. The results show that strains can effectively tune the bandgaps and RbSnCl3 is potential candidate for solar energy conversion and photocatalytic water splitting.